diarrhoea:  Diarrhoea means literally ‘through-flow’ (and hence semantically is a parallel formation to diabetes). It comes via late Latin diarrhoea from Greek diárrhoia, a term coined by the physician Hippocrates for ‘abnormally frequent defecation’. It was formed from the prefix dia- ‘through’ and rhein ‘flow’ (a relative of English rheumatism and stream).
Of other -rrhoea formations (or -rrhea, as it is generally spelled in American English), pyorrhoea ‘inflammation of the tooth sockets’ was coined in the early 19th century, and logorrhoea at around the turn of the 20th, originally as a clinical term in psychology (although subsequently hijacked as a facetious synonym for ‘talkativeness’). => rheumatism, stream